The present invention relates to improvements in form, fill and seal machines, and more particularly to a bag forming machine wherein an endless supply of plastic film with a zipper intermediate the edges is fed over a forming and filling tube and the edges sealed to form a tubular bag.
In a form, fill and seal operation, an endless continuous supply of film is brought forwardly and is shaped and wrapped around a filling and forming tube. The shaped film has its edges brought together and joined to form a tubular container. Contents are dropped through the filling tube into the container and cross-seals are formed to provide lengths of bags which are cut apart. In one method of forming bags in a form, fill operation, the film is provided with reclosable rib and groove zipper profiles extending longitudinally along the film parallel to the forming axis of the film. In the formation of the film into tubular form, the profiles can be joined as the bag is formed. It has been discovered that a stable operation can be accomplished by utilizing film where the profiles are already joined and are located intermediate the edges of the film. In this operation, the edges of the film are brought together to form a bottom seam for the bag. An example of a bag formation where the profiles are brought together is shown in Tilman U.S. Pat. No. 4,355,494. In U.S. Pat. No. 4,617,683, to Christoff and Ausnit, the formation of bags is illustrated where the raw edges of the film are joined, and in the present arrangement, a formation procedure such as that shown in the Christoff et al patent is employed with film being supplied where the interlocked profiles are located intermediate the edges of the film.
The packaging of products for retail sale and consumption has developed gradually over the years in order to enhance the ease with which the consumer can open the packaging in order to gain access thereto for use or consumption of the food product therein. In the form, fill and seal operation described above, such reclosable packages can be developed at relatively high manufacturing speed using an endless supply of film where the profiles are already extruded as part of the film and previously interlocked. In such packaging and package making, the containers are manufactured with the interlocking rib and groove profiles accurately and critically made so that they will protect the contents, such as foodstuffs, therein and yet be readily opened and reclosed. The profiles are made to be very relatively minute, and as such with accurate manufacturing tolerances, the shape and size of the profile must be accurately maintained and not distorted either in manufacture or in storage. It is a desirable attribute of such packaging that the bags be closed securely in an airtight manner to maintain freshness of a food product remaining within the package. The food products may be of varying types such as that which are packaged and stored within a box or carton which has the bag as an internal liner or pouch to contain dry cereal products. Other forms of packages or pouches can be made which are handled, stored and sold without a protective carton surrounding them.
The success of this type of packaging, which affords the customer with a reopenable package, relates to having mating flexible closure strips which interlock and do not afford leakage. Also, the flexible closure strips must be capable of being handled and reclosed easily. The success of such closures depends to a great extent upon avoiding deformities in the profiles while the material is being handled and particularly while it is being fed forwardly onto the forming machine and being completed by having the bottom seam and side seams formed.
In the formation of these pouches, the film is fed forwardly at production manufacturing speeds over the forming and filling tube. Acceptable manufacturing procedures require that the film be advanced intermittently with the advance stopped while the bottom seam and cross-seams are being formed. After the seams are formed, the film must again be accelerated so that a new pouch can be made after the previous one has been formed and filled. Such film advances must be accomplished without unnecessarily stressing and unnecessarily distorting the interlocked profiles. It has been found that distortion can easily occur while the film is drawn around curves or bends in the formation.
One location where distortion has occurred is in the location where the film is shaped over forming shoulders while being fed onto the forming tube. With the interlocked profiles located between the edges of the film, it is necessary to draw the film over relatively sharp forming edges. If the profiles are drawn with tension over such forming edges, the longitudinal tensions caused lateral forces on the film which tend to open the groove of the interlocked film. The groove is formed with side legs and a sharp pull on the film will tend to spread the legs of the groove to cause a distortion in the size and shape of the groove. This causes an insecure interlock and an insecure holding of the rib so that the rib and groove loses its efficiency and effectiveness.